This invention relates to hydrocarbon separation. More particularly, the invention concerns a process for separating oil and bitumen into group type fractions of asphaltenes, resins, aromatics and saturated hydrocarbons by high performance liquid chromatography.
Although there are an abundance of processes known to separate classes of hydrocarbons, accurate separation of whole oils and bitumens for geochemistry purposes was previously limited to open column separation methods. Such methods were complex and quite lengthy, involving up to several days to complete the separations.
High performance liquid chromatography (HPLC) methods were then developed for the group type fractionation of whole oils and bitumens. However, these methods require prior precipitation of the asphaltene fraction. Asphaltene precipitation is usually accomplished using a large excess of a linear saturated hydrocarbon, such as n-butane, n-pentane, n-hexane, and n-heptane. The solute is then fractionated into saturated hydrocarbon, aromatic hydrocarbon and resin groups by HPLC.
An inherent accuracy problem exists with such separation methods. The solubility of asphaltenes is sensitive to both the temperature and volume of the precipitating media. High molecular weight saturated hydrocarbons, aromatic hydrocarbons, and resins are sensitive to the same solubility effects as asphaltenes with the added problem of their being encapsulated or sequestered by the asphaltene precipitate. This precludes the recovery of some high molecular weight saturated hydrocarbons, aromatics, and resins. Such loss is unfortunate because valuable biomarker information is often contained in such high molecular weight hydrocarbon fractions.